Pyrometers used for remote measurement of temperature of a hot target by measuring the radiance emitted by the target are known to the art. However, such measurements cannot be made accurately without prior knowledge of the emissivity of target. Since the emissivity of any material not only depends upon the material composition and surface texture, but also may vary with the wavelength used by the pyrometer in making the measurement, as well as the viewing angle employed and even the temperature of the target, the emissivity is seldom if ever known with sufficient accuracy so that the measurement of temperature is error free.
The present invention is directed toward a new type of pyrometer wherein prior knowledge of the target emissivity is not needed or utilized and wherein the emissivity uncertainty is eliminated by direct and in situ measurement of the ratio of reflectivites of the target at two different wavelengths of measurement.